The most widely used refuse disposal methods comprise those which have the object of transforming the refuse into fertilizer and are essentially based on so-called composting or refuse compost, a kind of anaerobic fermentation.
Such composting can be effected in a "natural" or industrial manner. The first case involves storage of the discharged refuse with the formation of solid heaps which are covered with mould and in which, after a certain fermentation time, the organic parts are transformed into humus containing quantities of nitrogen, phosphorus and potassium which, although they are very low, allow this to be used as organic fertilizer.
The sites destined for the discharges are always large, must be appropriately equipped and prearranged for preventing, for example, pollution of subterranean water tables, require the employment of personnel and means of non-negligible importance and also always involve air pollution problems.
Moreover, completion of the anaerobic fermentation phase always requires not less than 5-6 months.
In the second case, the industrial method involves subjecting the refuse to a preliminary sifting to remove metal parts and to separate out paper, rags, plastics, glass and the like. The remainder is, after appropriate crushing, caused to ferment as in the case of natural fermentation with the respective disadvantages, or the fermentation is primed with suitable cultures in fermentation cells, rotary drums and the like. The time taken for completion of the fermentation is in this case never less than 15-20 days.
Other refuse disposal techniques involve their combustion and are notoriously uneconomical to carry out, and require complicated plant and equipment, which are expensive both in terms of operation and in terms of control; or they involve destruction by chemical attack, which has not met with any success in practice because of the high costs and the recognized technical disadvantages.
Dry distillation to produce coal gas, tar and coke has also been attempted. This technique was promptly abandoned, because it is entirely uneconomical and highly polluting.